Function looksJSON

transpiler/transform/operators.go:656–693

looksJSON reports whether a node is syntactically JSON: a cast to json/jsonb, a JSON-returning json* function call (including the json_extract calls this transform produces from -> / ->>), a JSON-producing conversion function (to_json/to_jsonb/row_to_json/array_to_json), or a `->` A_Expr (which this

(node *pg_query.Node)

// `json_extract_string(d,'a') || 'x'` is plain text concat in Postgres and
// must stay that way (likewise `->>`, which yields text, does not count).
func looksJSON(node *pg_query.Node) bool {
	if node == nil {
		return false
	}
	if tc := node.GetTypeCast(); tc != nil && tc.TypeName != nil && len(tc.TypeName.Names) > 0 {
		if last := tc.TypeName.Names[len(tc.TypeName.Names)-1].GetString_(); last != nil {
			switch strings.ToLower(last.Sval) {
			case "json", "jsonb":
				return true
			}
		}
	}
	if fc := node.GetFuncCall(); fc != nil && len(fc.Funcname) > 0 {
		if last := fc.Funcname[len(fc.Funcname)-1].GetString_(); last != nil {
			name := strings.ToLower(last.Sval)
			if strings.HasPrefix(name, "json") && !jsonFuncReturnsNonJSON(name) {
				return true
			}
			// JSON-producing conversions whose names don't start with "json".
			// FunctionTransform (which runs earlier) maps to_jsonb -> to_json,
			// but cover the Postgres spellings too for direct/standalone use.
			switch name {
			case "to_json", "to_jsonb", "row_to_json", "array_to_json":
				return true
			}
		}
	}
	// A bare `d -> 'a'` operand (no cast, not yet rewritten): the arrow always
	// becomes json_extract, which returns JSON. Without this, `(d->'a') ||
	// (d->'b')` would fall through to DuckDB string concat of two JSON values.
	if ae := node.GetAExpr(); ae != nil && ae.Kind == pg_query.A_Expr_Kind_AEXPR_OP &&
		ae.Lexpr != nil && ae.Rexpr != nil && len(ae.Name) == 1 {
		if s := ae.Name[0].GetString_(); s != nil && s.Sval == "->" {
			return true
		}
	}
	return false
}

// jsonFuncReturnsNonJSON reports whether a json*-named function returns a
// non-JSON value (VARCHAR, BIGINT, BOOLEAN, ...), so its result concatenated